Methods of filling a die cavity with multiple materials for powder metal compaction

ABSTRACT

A method of making powder metal compacted parts of multiple dissimilar materials. A die insert is provided having a pattern of cavities corresponding in shape to the shape of a die cavity. The pattern of cavities are filled with two or more dissimilar powder metals which are subsequently pressed within the die cavity to form a compacted powder metal part having at least two discrete regions of dissimilar material.

FIELD OF THE INVENTION

[0001] This intention relates to composite part manufacturing by powder metallurgy processing

BACKGROUND OF THE INVENTION

[0002] Powder metallurgy is the branch of metallurgy related to the manufacture of metal powders and articles fabricated from metal powders by the application of forming and sintering processes. Conventional compaction and sintering is the most widely employed technique for producing powder metallurgy parts. In this conventional process, elemental or alloy metal powders are mixed with additives, such as graphite or die lubricants, and the premix is fed into a die cavity where it is subjected to either warm compaction or cold compaction. This compaction may be a single-action pressing, in which the powder is pressed in a stationary die between one moving and one fixed punch, or may be a double-action pressing in which the powder is pressed in a die between two punches moving from opposite directions into the die cavity. The resulting pressed part is referred to as a green part. The green part is then ejected from the die and sent to a sintering furnace wherein the neighboring particles within the mass of powder bond together due to the application of heat.

[0003] The powder metallurgy technique has proven useful for the production of mass quantities of low complexity shaped parts made of a single material. However, there are numerous fields that employ composite parts of two or more dissimilar materials that do not enjoy the benefits of powder metallurgy techniques. There is thus a need for the powder metallurgy process to be adapted to production of composite parts comprising multiple dissimilar materials.

SUMMARY OF THE INVENTION

[0004] The present invention provides a method of making composite powder metal parts in which a die is filled according to a desired pattern of two or more dissimilar materials, followed by pressing the powder metals to form a compacted powder metal part having at least two discrete regions of dissimilar material. In one example of the present invention, a die insert is provided having a pattern of cavities in a shape corresponding to the shape of the die cavity and the die insert is placed within the cavity for filling the powder metals. The selected powder materials should be similar in fill, for example, should have similar apparent densities. The die insert is then removed from the cavity and the powders pressed within the die cavity. In an alternative example of the present invention, a similar die insert having the pattern of cavities is placed on the top surface of the die over a lower punch positioned in an ejection position. The die insert is then filled with the powder metals. Upon lowering of the die punch, the powder metals filled in the die insert are drawn into the die cavity formed as the punch lowers. The powders are then pressed in the die cavity. By the method of the present invention, composite powder metal parts may be produced having multiple dissimilar materials in different regions of the part.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.

[0006] FIGS. 1A-1D schematically depict in partial cross-section a method of the present invention for fabricating a powder metal compacted part of three similar materials;

[0007]FIG. 2 is a perspective view of an insert for use in a method of the present invention:

[0008]FIG. 3 is a plan view of a composite powder metal component of the present invention;

[0009]FIG. 4 is a perspective view of an inner bowl and outer bowl of a hopper that may be used for the filling aspect of the present invention;

[0010] FIGS. 5A-5E are cross-sectional schematic views of a method of the present invention using the insert of FIG. 2 and the hopper of FIG. 4 to produce the component of FIG. 3; and

[0011] FIGS. 6A-6D schematically depict in partial cross-section an alternative method of the present invention for fabricating a powder metal compacted part of three dissimilar materials.

DETAILED DESCRIPTION

[0012] The present invention provides a method for fabricating composite powder metal compacted parts. To this end, and in accordance with the present invention, a die insert is provided having cavities in a pattern corresponding to the desired part configuration and corresponding to the shape of a die cavity configured to press powder metal to form the desired part. At least two different cavities of the die insert are concurrently or sequentially filled with at least two different powder metals. The powder metals are separated from the die insert, leaving the powders in the desired pattern in the die cavity. The powder metals are then pressed in the die to form a compacted powder metal part. This compacted powder metal part may then be sintered to high density by known sintering techniques to form a single-piece powder metal part of high structural stability having discrete regions of at least two dissimilar materials.

[0013] In one embodiment of the present invention, the insert cavities are filled concurrently with the two or more different powder metals, which are then each concurrently pressed. In another embodiment of the present invention, the insert cavities are filled sequentially with one powder metal after another, each powder being pressed before the next is filled. In other words, one powder metal is filled into one or more cavities then pressed; then a second powder metal different than the first is filled into one or more different cavities then pressed; and so on until all the desired cavities are filled. The insert is then removed. The entire part may then be pressed in the die cavity to form the compacted part.

[0014] By the term dissimilar, it is meant that the powder metals have different compositions. For example, low carbon steel and stainless steel are dissimilar. As a further example, pure iron, iron with 0.2% phosphorus, and iron with 0.3% phosphorus are all dissimilar. However the dissimilar powder metals should be similar in fill. For example, dissimilar powder metals that have similar apparent densities (i.e., weight of a unit volume of material) will behave similarly in fill.

[0015] The pressing of the filled powder metal may be accomplished by uniaxially pressing the powder in a die, for example at a pressure of about 45-50 tsi. It should be understood that the pressure needed is dependent upon the particular powder metal materials that are chosen. In a further embodiment of the present invention, the pressing of the powder metal involves heating the die and/or heating the powders for warm compaction. For example, for pressing iron-based powder metals, the die is heated to a temperature in the range of about 275° F. (135° C.) to about 290° F. (143° C.), and the iron-based powders within the die are heated to a temperature in the range of about 175° F. (79° C.) to about 225° F. (107° C.).

[0016] In an embodiment of the present invention, the compacted powder metal part, or green compact, is sintered. For iron-based powder metals, sintering generally comprises heating the compacted powder metal to a first temperature of about 1400° F. (760° C.) and holding at that temperature for about one hour. Generally, the iron-based powder metals include a lubricating material, such as a plastic, on the particles to increase the strength of the material during compaction. The internal lubricant reduces particle-to-particle friction, thus allowing the compacted powder to achieve a higher green strength after sintering. The lubricant is then burned out of the composite during this initial sintering operation, also known as a de-lubrication or delubing step. A delubing for one hour is a general standard practice in the industry and it should be appreciated that times above or below one hour are sufficient for the purposes of the present invention if delubrication is achieved thereby. Likewise, the temperature may be varied from the general industry standard if the ultimate delubing function is performed thereby. After delubing, the sintering temperature is raised to a full sintering temperature, which is generally in the industry about 2050° F. (1121° C.) for iron-based powders. During this full sintering, the compacted powder shrinks, and particle-to-particle bonds are formed. Standard industry practice involves full sintering for a period of one hour, but it should be understood that the sintering time and temperature may be adjusted as necessary. The sintering operation may be performed in a vacuum furnace, and the furnace may be filled with a controlled atmosphere, such as argon, nitrogen, hydrogen or combinations thereof. Alternatively, the sintering process may be performed in a continuous belt furnace, which is also generally provided with a controlled atmosphere, for example a hydrogen/nitrogen atmosphere such as 75% H₂/25% N₂. Other types of furnaces and furnace atmospheres may be used within the scope of the present invention as determined by one skilled in the art.

[0017] For purposes of illustrating the method of the present invention, FIGS. 1A-1D schematically depict a first example of a method of the present invention for forming a powder metal compacted part of multiple dissimilar materials. In this method, a die insert 10 is used that fits inside of the die cavity 12 of die 14. This insert 10 may be made out of any material and may be fabricated by any suitable process. The insert 10 contains a pattern of cavities 16,18,20, in this example three cavities, to hold the different powder metal materials. At least two different powder metals are used in the present invention to form a composite part having at least two dissimilar materials. In this example, as shown in FIG. 1A, three different powder metals 17,19,21 are used. The powder metal materials 17,19,21 may be filled into the cavities 16,18,20 of the die insert 10 by any suitable method. The powders 17,19,21 may be filled concurrently or sequentially. When filling is complete, die insert 10 is lifted out of the die cavity 12 by any suitable method, as shown in FIG. 1B. The removal of the insert 10 causes some settling of the powder, as further depicted in FIG. 1B. The upper punch 22 of the press 24 is then lowered down upon the powder-filled die cavity 12, as shown by the arrow in FIG. 1B, to uniaxially press the powders 17,19,21 in the die cavity 12, as shown in FIG. 1C. The final composite part or green compact 26 is then ejected from the die cavity 12 by raising the lower punch 28, as shown in FIG. 1D. According to known powder metallurgy techniques, this green compact 26 may be then transferred to a sintering furnace (not shown).

[0018] Where the filling of the powder metals 17,19,21 is sequential, the first powder metal 17 is filled into one or more of the insert cavities 16, and a specially configured upper punch 22 is lowered so as to press the filled powder 17. The second powder metal 19 is then filled into one or more of the insert cavities 18 and a specially configured upper punch 22 lowered to press the second powder 19. This process is continued until all powder metals 17,19,21 are filled into the appropriate insert cavities 16,18,20. The insert (10) is then removed and the entire part 26 may then be pressed further in the die cavity 12. The insert 10 may be removed before or after the last powder metal 21 is compacted.

[0019] FIGS. 2-5E further depict a die insert, a powder metal component, a hopper configuration and a pressing technique that may be used to achieve concurrent filling or sequential filling of two powder metals and subsequent compaction to form the composite powder metal part of the present invention. It is to be understood, however, that these illustrations are merely an example of a possible method for carrying out the present invention.

[0020]FIG. 2 depicts a die insert 30 having cavities 32 and 34 that may be placed within a die cavity to produce a powder metal disk 36 as shown in FIG. 3. Disk 36 comprises two powder metals 33,35 that are compacted to form discrete segments 38,39. The two powder metals 33,35 are filled concurrently or sequentially into the separate insert cavities 32,34, and then the insert 30 is removed. By way of example only, FIG. 4 depicts a hopper assembly 40 that may be used to fill the insert 30 of FIG. 2 with the powder metals 33,35. In this assembly 40, an inner bowl 42 is provided having arc tubes 44 for forming the generally arcuate segments 39 of the composite part or metal disk 36 of FIG. 3. This inner bowl 42 is adapted to hold and deliver one of the two powder metals. An outer bowl 46 is positioned around the inner bowl 42, with the outer bowl 46 adapted to hold and deliver the second powder metal for forming the generally arcuate segments 38. This dual hopper assembly 40 enables either concurrent or sequential filling of the die insert 30 of FIG. 2.

[0021] FIGS. 5A-5E depict schematic views in partial cross-section of how the die insert 30 of FIG. 2 and the hopper assembly 40 of FIG. 4 can be used with an uniaxial die press 50 to produce the composite powder metal disk 36 of FIG. 3. In this method, the insert 30 is placed within a cavity 52 in the die 54, as shown in FIG. 5A, with a lower punch 56 of the press 50 abutting the bottom 30 a of the insert 30. The hopper assembly 40 is placed over the insert 30 and the powder metals 33,35 are filled into the insert cavities 32,34, concurrently or sequentially, as shown in FIG. 5B. The hopper assembly 40 is then removed, leaving a filled insert 30 in the die cavity 52, as shown in FIG. 5C. Then the insert 30 is lifted out of the die cavity 52, which causes some settling of the powder, as seen in FIG. 5D. The upper punch 58 of the press 50 is then lowered down upon the powder-filled die cavity 52, as shown by the arrow in FIG. 5D to uniaxially press the powders in the die cavity 52. The final composite part 60 is then ejected from the die cavity 52 by raising the lower punch 56. Where the filling is sequential, the first powder is poured into either the inner bowl 42 or outer bowl 46, and a specially configured upper punch 58 is lowered so as to press the filled powder. The second fill is then effected and the insert 30 removed for pressing and ejection of the complete part 60.

[0022] A second example of the method of the present invention is depicted schematically in FIGS. 6A-6D. In this method, the die insert 10′ is placed on a top surface 15 of the die 14 over the die cavity 12. The lower punch 28 is placed in the ejection position, as shown in FIG. 6A. The pattern of cavities 16,18,20 in the die insert 10′ lies directly above the lower punch 28. The powder metals 17,19,21 are then filled into the die insert 10′, either concurrently or sequentially, as in the previous embodiments. The lower punch 28 is then lowered to a non-ejection position, as shown in FIG. 6B. The lowering of the punch 28 forms a vacuum which pulls the powder metals 17,19,21 out of the bottom 10 a′ of the insert 10′ and into the die cavity 12. The insert 10′ is then removed from the top surface 15 of the die 14,. and the upper punch 22 of the die 14 is lowered into the die cavity 12 to compact the powder metals 17,19,21, as shown in FIG. 6C. The lower punch 28 is then raised to eject the final composite part or green compact 26. as shown in FIG. 6D.

[0023] In one embodiment of the present invention, pneumatic air hammers or tappers (not shown) may be placed on, in, or around the die inserts used in any of the methods described and depicted above. The vibrating of the die insert enables the powder metals to flow out of the insert with greater ease as the insert is removed from the die cavity, or as the powder metals are drawn out of the bottom of the insert into the die cavity. The vibrating further enables a greater tap density. In another embodiment of the present invention, a lubing agent, such as a dry lube, is sprayed or added to the inside surfaces of the insert cavities used in any of the above methods. Again, this dry lube helps to improve the flow of the powder metals out of the die insert. In yet another embodiment of the present invention heaters and thermocoiples (not shown) may be used in conjunction with the die insert. The heat keeps the powder warm, if warm compaction is being optimized, and again allows the powder metals to more easily flow out of the die insert.

[0024] The above methods have been described with respect to a single-action pressing. It is to be understood, however, that double-action pressing may be used in any of the methods described above. Further, while various examples have been given of die inserts, the present invention may be used to form any part that requires two or more dissimilar powder metal materials, whatever the specific pattern desired. Thus, the invention should not be limited to the particular examples described above.

[0025] While the present invention has been illustrated by the description of embodiments thereof and awhile the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, variations in the hopper assembly, filling method, (lie inserts and cavity patterns may be employed to achieve a composite powder metal part of the present invention. The invention in its broader aspects is therefore not limited to the specific details, representative apparatuses and methods and illustrative examples shown and described. Accordingly, departures may be made from such details Without departing from the scope or spirit of applicant's general inventive concept. 

What is claimed is:
 1. A method of making a powder metal compacted part of multiple dissimilar materials, the method comprising: providing a die insert having a pattern of cavities, the pattern having a shape corresponding to a shape of a die cavity in a die; filling at least two different cavities of the die insert with at least two respective dissimilar powder metals; separating the powder metals from the die insert so as to position the powder metals in their filled pattern in the die cavity; pressing the powders in the die cavity to form a compacted powder metal part having at least two discrete regions of dissimilar material.
 2. The method of claim 1, wherein the die insert is provided on a top surface of the die over a lower punch positioned in an ejection position, and the separating occurs by lowering the lower punch to draw the powder metals from the die insert into the die cavity formed by lowering the punch.
 3. The method of claim 1, wherein the die insert is placed in the die cavity prior to the filling, and the separating occurs by lifting the die insert out of the die cavity.
 4. The method of claim 1, wherein each of the at least two powder metals are filled concurrently.
 5. The method of claim 1, wherein each of the at least two powder metals are filled sequentially with each powder metal being pressed after each filling step.
 6. The method of claim 1, wherein the insert is vibrated to facilitate separation of the powder metals from the die insert.
 7. The method of claim 1, wherein a lubing agent is applied to interior surfaces of the insert cavities prior to filling to facilitate separation of the powder metals from the die insert.
 8. The method of claim 1, wherein the die insert is heated to facilitate one or both of separation of the powder metals from the die insert and compaction of the powders in the die cavity.
 9. The method of claim 1, wherein the pressing comprises uniaxially pressing the powders in the die cavity.
 10. The method of claim 1, wherein the pressing comprises pre-heating the powders and pre-heating the die.
 11. The method of claim 1, further comprising sintering the compacted powder metals.
 12. A method of making a powder metal compacted part of multiple dissimilar materials, the method comprising: providing a die insert having a pattern of cavities, the pattern having a shape corresponding to a shape of a die cavity in a die; filling one or more first cavities of the die insert with a first powder metal; pressing the first powder metal in the die insert to compact the first powder metal; repeating the steps of filling and pressing, each time with a different powder metal, until the desired number of powder metals have been filled; separating the powder metals from the die insert so as to position the powder metals in their filled pattern in the die cavity; pressing the powders in the die cavity to form a compacted powder metal part having at least two discrete regions of dissimilar material.
 13. The method of claim 11 wherein the die insert is provided on a top surface of the die over a lower punch positioned in an ejection position, and the separating occurs by lowering the lower punch to draw the powder metals from the die insert into the die cavity formed by lowering the punch.
 14. The method of claim 12, wherein the die insert is placed in the die cavity prior to the filling, and the separating occurs by lifting the die insert out of the die cavity.
 15. The method of claim 12, wherein the insert is vibrated to facilitate separation of the powder metals from the die insert.
 16. The method of claim 12, wherein a lubing agent is applied to interior surfaces of the insert cavities prior to filling to facilitate separation of the powder metals from the die insert.
 17. The method of claim 12, wherein the die insert is heated to facilitate one or both of separation of the powder metals from the die insert and compaction of the powders in the die cavity.
 18. The method of claim 12, wherein the pressing comprises uniaxially pressing the powders in the die cavity.
 19. The method of claim 12, wherein the pressing, comprises pre-heating the powders and pre-heating the die.
 20. The method of claim 12, further comprising sintering the compacted powder metals.
 21. A method of making a powder metal compacted part of multiple dissimilar materials, the method comprising: placing a die insert in a die cavity, the die insert having a pattern of cavities; filling at least two different cavities of the die insert with at least two respective dissimilar powder metals; lifting the die insert out of the die cavity; and pressing the powders in the die cavity to form a compacted powder metal part having at least two discrete regions of dissimilar material.
 22. The method of claim 21, wherein each of the at least two powder metals are filled concurrently.
 23. The method of claim 21, wherein each of the at least two powder metals are filled sequentially with each powder metal being pressed after each filling step.
 24. The method of claim 21, wherein the insert is vibrated to facilitate separation of the powder metals from the die insert.
 25. The method of claim 21, wherein a lubing agent is applied to interior surfaces of the insert cavities prior to filling to facilitate separation of the powder metals from the die insert.
 26. The method of claim 21 wherein the die insert is heated to facilitate one or both of separation of the powder metals from the die insert and compaction of the powders in the die cavity.
 27. The method of claim 21, wherein the pressing comprises uniaxially pressing the powders in the die cavity.
 28. The method of claim 21, wherein the pressing comprises pre-heating the powders and pre-heating the die.
 29. The method of claim 21, further comprising sintering the compacted ponder metals.
 30. A method of making a powder metal compacted part of dissimilar materials, the method comprising: providing a die having a lower punch positioned in an ejection position; providing a die insert on a top surface of the die over the lower punch, the die insert having a pattern of cavities with a shape corresponding to a shape of a die cavity formed when the lower punch is in a non-ejection position; filling at least two different cavities of the die insert with at least two respective dissimilar powder metals; lowering the lower punch of the die from the ejection position to the non-ejection position to draw the powder metals from the die insert into the die cavity in their filled pattern; pressing the powder metals in the die cavity to form a compacted powder metal part having at least two discrete regions of dissimilar material.
 31. The method of claim 30, wherein each of the at least two powder metals are filled concurrently.
 32. The method of claim 30, wherein each of the at least two powder metals are filled sequentially with each powder metal being, pressed after each filling step.
 33. The method of claim 30, wherein the insert is vibrated to facilitate separation of the powder metals from the die insert.
 34. The method of claim 30, wherein a lubing agent is applied to interior surfaces of the insert cavities prior to filling to facilitate separation of the powder metals from the die insert.
 35. The method of claim 30, wherein the die insert is heated to facilitate one or both of separation of the powder metals from the die insert and compaction of the powders in the die cavity.
 36. The method of claim 30, wherein the pressing comprises uniaxially pressing the powders in the die cavity.
 37. The method of claim
 30. wherein the pressing, comprises pre-heating the powders and pre-heating the die.
 38. The method of claim 30, further comprising sintering the compacted powder metals. 